A recent trend in the office-equipment industry is to provide "multi-function" devices, in which the functions of a copier and printer, and sometimes a facsimile machine and digital scanner as well, are combined in a unified architecture. In the basic case of a combined copier-printer, such a machine operates as a typical printer, in that digital image data, such as originating in a computer, can be submitted to the apparatus, and result in the output of print sheets based on the digital data. In addition, hard-copy originals can be placed in a document handler and then scanned, so that the images on the hard-copy originals are exposed onto one or more photosensitive chips (such as a CCD) to yield a quantity of digital image data. This digital image data based on the scanned hard-copy originals can then be submitted to the same printing hardware at which the print jobs are output. Thus, in a copier-printer, a single set of printing hardware is shared by a printing apparatus and a copier. If a facsimile function is added, incoming faxes are printed on the same printing hardware, and the digital scanner can be used for scanning outgoing faxes.
In one common architecture for a copier-printer, the control system governing the copier functions is distinct from the control system covering the printer functions. Typically, but not necessarily, there will be in a single architecture one CPU dedicated to distinctly printer functions, and another dedicated to copier functions Among the functions performed by the printer CPU are functions relating to what can generally be called "rasterizing" original image data. By "rasterizing" is typically meant decomposing original image data which is in a page description language, such as a Adobe.RTM. PostScript.TM. or PCL; rasterization can also include interpreting data which is originally in TIFF, ASCII, or a facsimile format. The result of this rasterization, regardless of the format of original data, is a set of image data which is largely directly operative of printing hardware, such as binary data compressed according to a relatively simple algorithm.
Further, in such a two-CPU architecture, the copier functions are largely controlled by a copier CPU. The copier CPU accepts data from the hard-copy scanner. As the image data from the scanner was never originally in a page description language or other format, the rasterizing functions of the printer CPU are irrelevant to the copying process. Within the copier-printer, individual page images are temporarily retained in a memory until a particular moment in which the image data needs to be submitted to the printing hardware. Once the image data is rasterized and ready to be submitted to the hardware, it is immaterial whether the rasterized image data originated as a "print job" or a "copy job."
One practical advantage of the copier-printer architecture is that the scanner associated with the copier portion of the architecture can be used not only to directly submit image dated to the printer hardware for copying, but can also be used for other purposes. For example, the input scanner can be used by itself as an input scanner for a facsimile apparatus; in this case, hard-copy original input at the input scanner will in effect cause a set of printing hardware at another apparatus, over phone lines, to print out the image. Other uses of the input scanner include a "scan-to-file" function, in which, instead of having the image data immediately used for making a copy, retaining the image data in a computer for an indefinite period of time. Once in a computer, the scanned-in data can be converted (such as through a optical character recognition program) into a searchable text format. In a highly-networked system, the original image can be scanned in at one copier-printer and (simultaneously, or at some time in the future) printed out at many different remote copier-printers. In short, the copier-printer architecture enables the input scanning and output printing functions to be disassociated in both space and time.
Many of the business opportunities afforded by the copier-printer architecture can be exploited in what can be called a "copy shop environment" which includes not only retail copy shops but public or university libraries. In the copy-shop environment it is typical to charge retail users for individual "uses" of a machine. In the context of analog copiers, in which a scanned or exposed input necessarily implies an output print, auditing or otherwise making payment for copy-shop functions was straightforward. In a digital, copier-printer context, because the input scanning and output printing functions are not immediately related, it becomes more complicated to facilitate charging and paying for the various scanning and printing functions available to a retail user. The present invention is directed toward an auditing system which enables monitoring of both input scanning and output printing with a digital copier-printer in a copy-shop environment.